Fuel admission applications for large stationary internal combustion industrial engines have been handled in the past by mechanically actuated valves capable of developing rather large valve actuating forces which were thought necessary for the pressures and flow rates encountered in such applications. Although, it would be desirable to provide an electrically actuated fuel admission valve for such applications, the perceived need for high actuating forces combined with fast, reliable actuation have weighed against this development. Moreover, although electrically actuated fuel admission valves have been used in small engine applications, the technology is not readily transferable to the much larger industrial engines. Indeed, providing an electrically actuated gaseous fuel admission valve for very large engines cannot be accomplished by simply scaling up an electrically operated fuel admission valve for a smaller application, such as an automotive engine, because the pressures, flow rates, and power for the large, industrial engines--often on the order of thousands of horsepower--present an application which is substantially different in kind than the automotive.
In general, the large industrial engines of the past have been either single fuel (such as diesel or natural gas, for example) or multiple fuel (capable of running on either of those fuel sources). The ability to precisely control the admission of fuel to each cylinder of a multiple cylinder engine for such applications is very important because balanced firing of all of the cylinders will reduce both engine vibrations and engine wear. In addition, balanced firing will result in improved fuel economy and reduced emissions--important considerations in a society of limited natural resources and heightened sensitivity to environmental issues. Similarly, it can be seen that the valve open time (dwell time), the precise point of opening with respect to rotation of the cam shaft, and the precise point of closing, are also very important in monitoring and controlling the output of the engine. Thus, it is desirable to provide a valve which is easily monitored and individually adjustable within an engine to achieve efficient operation.
Both the steady state and operating characteristics of the valve itself are important in determining its flow characteristics. The steady state characteristic, namely the size of the port or ports within the valve, is the major component in determining fuel flow. However, in a fuel admission application, it is desirable to pass the same amount of fuel through the individual valve assemblies every cycle to achieve the balanced firing and consistent operation mentioned above. Thus, even though the individual valves admit less fuel into the engine during the opening and closing stages of their cycles than during the fully open stage, it is important that the amount of fuel admitted during these transition periods is the same from cycle to cycle. Consequently, the operating characteristics of the valve assemblies must be substantially constant such that the opening and closing of the valve is consistent from cycle to cycle.
In the past, large industrial engines have used mechanically or hydraulically actuated valves in order to achieve the necessary flow rates at the pressures involved. For example, it is not unusual to provide cam driven valves which are mechanically opened and closed by a cam shaft driven by the engine itself. Timing with respect to the engine and adequate force for opening and closing the valve in a repeatable fashion is thus readily achieved. However, they are achieved at a rather significant expense in the mechanics of the system. In short, this technique requires a great deal of additional hardware with attendant repair and replacement costs. Furthermore, it is difficult to adjust the dwell time on an individual valve basis, or to provide the control necessary for switching the engine from one type of fuel to another.
In other approaches, hydraulically actuated fuel valves have been utilized to give greater flexibility in admission while still providing the necessary force for operation. Thus, an electrical signal may operate an electrical pilot valve which controls a hydraulic circuit, and the hydraulic circuit then opens and closes the hydraulically actuated fuel control valve. While an approach of this type can give greater flexibility in adjusting the dwell time, for example, it is cumbersome in that it requires a high pressure source of hydraulic fluid in order to achieve fast response. The high pressure source requires a pump (often driven by an associated electric motor), a filtration system, a cooling system, a sump, a regulation system, pipes, return lines and a litany of other components. Thus, this approach requires an excessive amount of additional hardware which translates into additional expenses both in the initial investment and in repair and maintenance of the system.